Apparatus for detecting and estimating inflammable gases in air



Oct. 4, 1932. A. N. ERICKSON 1,880,941

APPARATUS FOR DETECTING AND ESTIMATING INFLAMMABLE GASES IN AIR FiledApril 5, 1927 2 Sheets-Sheet 1 FIG. 2.,

1N VEN TOR.

ll'r fi ATTORNYS.

Oct. 4, 1932. A. N. ERICKSON 1,880,941 APPARATUS FOR DETECTING ANDESTIMATING INFLAMMABLE GASES IN AIR Filed April 5, 1927 2 Sheets-Sheet 2FIG. 3.

INVENTOR:

ATTORNEYS.

Patented Oct. 4, 1932 UNITED STATES PATENT OFFICE ALBERT N. ERICKSON, OFELMHURST, NEW YORK, ASSIGNOR TO UNION CARBIDE COM- PANY, OF NEW YORK, N.Y., A CORPORATION OF VIRGINIA APPARATUSFOR DETECTING AND ESTIMATINGINFLAMMABIIE GASES IN AIR Application filed April 5, 1927. Serial No.181,227.

My invention relates to a process and apparatus for determining thecontent of combustible gas in gaseous mixtures and is especially adaptedfor use in coal or other mines, although it is equally well adapted fordetecting the presence of inflammable vapors in receptacles which havecontained oils, or for use in any other. situation in which it isdesirable to determine the presence of combustible or inflammableconstituents in an atmosphere.

Combustible gases when mixed with air \or other gases containing oxygenand brought into contact with a heated surface, will begin to oxidize atatemperature below the ignition point of the mixture. Furthermore, whenin contact with a heated surface oxi- (lation of the inflammable orcombustible gases will occur, even though the latter is present in aproportion too small to support free combustion. Oxidation of theinflammable gas even below its ignition temperature is accompanied bythe generation of heat, part of which will act to raise the tem peratureof the surface in contact with which the oxidation is proceeding. If theproportion of combustible gases in the mixture be great enough it willgenerate enough heat to maintain the temperature of the surface, butmore dilute mixtures require the supply of extraneous heat. In eithercase the surface will assume a higher temperature in air containing acombustible gas.

These well-known properties have been utilized in the construction ofdevices for detccting the presence or estimating the proportion ofinflammable gases in mixtures. I11 most ofsuch devices a filament ofplatinum wire heated by the passage of electrical current has been themeans for providing the oxidizing surface although such substances asclays have been used. In the devices hitherto known it has been thepractice to rely upon a catalytic effect, the temperature of the heatingsurface being only sufficient to bring about catalysis. To permit alower temperature to be used the normal catalytic property of wroughtplatinum has been augmented by applying a coating of finely dividedplatinum or other catalytic substances. The increase in temperature inthe presence of com bustible gas has been measured by a thermocouplehaving its junction in close proximity to the filament, by the use of aresistance element, or by visual inspection.

In my device, I take advantage of the diminishing electricalconductivity of a metallic filament as its temperature rlses, andascertain its increased resistance, and thereby the increasedtemperature, by the principle of the Wheatstone bridge. Furthermore, Ido not employ a separate resistance element for this purpose but use thesame element which is heated to cause the oxidation. This element isheated to such a temperature that catalytic action becomes superfluous,thereby avoiding the inaccuracies due to poisoning of a catalyticheating element. I have found platinum wire to be Very satisfactory asthe testing filament by reason of its fairly high electrical resistance,its large temperature-resistance coefficient, its high melting point andits resistance to oxidation at high temperatures.

An object of my invention is to produce a portable device for testingfor the presence of inflammable gases in air, which shall be sensitiveto the presence of one half of one percent of methane, in an atmosphere,which shall be rapid in operation, and shall permit of an exploration ofpockets into which the operator cannot enter.

These and other objects of my invention will be apparent from thefollowing description of one embodiment thereof taken in connection withthe accompanying drawin s in which igure 1 is a diagram of theelectrical connections;

Figure 2 is a schematic representation of the testing box; and

Figure 3 is a vertical cross-section of'the testing element and itsprotective enclosure.

A platinum filament A with its connecting leads forms one leg of theWheatstone bridge, fixed resistances B and C forming two other legs ofthe bridge, the latter resistances preferably being formed of a wirehaving a small temperature-resistance coefiicient such as nichrome. Thefourth leg is formed of a 'any inflammable gas. I may use thisresistance for bringing the bridge back into balance 1 after thefilament A has' come into contact with the inflammable gases, but Iprefer to measure the change irr resistance by noting the amount ofunbalance. For this purpose an instrument for indicating the flow'ofsmall currents is connected across the bridge in the usual manner, theconnection being provided with a switch I. Instrument G may be either agalvanometer, a millivoltmeter, or a milliammeter. The current for theoperation of the bridge is furnished by any convenient source F. Such asource may conveniently be a storage battery of the type used forsupplying current to miners cap lights. A switch H is provided forcontrolling this current and a resistance E having a high temperaturecoefiicient is also inserted in the circuit to maintain a constantcurrent flow.

I may employ various resistances in the bridge but the following havegiven satisfactory results. The resistance A consists'of 1 of No. 36platinum wire having a resistance of 0.375 ohm at 25 C., and 1.647

ohms at 1035 C. The resistance B has a.

value of 14.236 ohms; the resistance 0 a value of 3.321 ohms; the fixedportion of resistance D has a value of 0.375 ohm and the variableportion has an average resistance of 0.01 ohm. With these resistances Ihave found that the current drain will be 1.85 amperes at 3.65 voltsfrom a miners lamp storage battery, which batteries are usually capableof supplying a current of 2 amperes at 4 volts for at least three hours.Using such a current and a millivoltmeter at G, I have observed thefollowing potential differences between the opposite sides of the bridgewith the stated percentages of methane mixed with air.

Methane Millivolts Per /gent 7 1 13 2 25 3 35 4 42. 5 5 49 to bedescribed hereafter is connected in any suitable manner such as by aplug K.

The resistance A of platinum wire is mounted in a. testing element shownin Fig ure 3. The resistance itself consists of a piece of platinum wireand may be either straight or coiled. The latter allows a higher initialtemperature to be obtained with the same flow of current. I have foundthat using 1% of No. 36 platinum wire good results are obtained when thewire is wound .into a coil in diameter and long. In order to permit ofthe replacementof filaments I find it convenient tomount the wire in aholder, thus permitting greater facility in the replacement of adestroyed filament and insuring that all. filaments shall have as nearthe same resistance as possible. However, it should be noted that aprecise equivalence in resistance is not essential since the variableresistance D affords a means for maintaining the bridge in balance inspite of variation in filament resistance due to the use of difierentfilaments or changes which may take place during the life of a singlefilament. The filament is held by screws Y in end caps Z. These end capsare spaced apart by a member U which may be of metal or may be made ofany non-conductive substance capable of resisting heat such, forexample, as transite. In case the wall is madeof metal an insulatingplug V is provided to prevent the short-circuiting of the filament bythe spacing member U. In either case the wall U is slotted in suchmanner as to permit free ingress of the surrounding atmosphere. Thisalso serves to reduce the mass of material in close proximity to thefilament to the smallest amount necessary to provide the mechanicalstrength necessary to reduce breakage. The end members Z are providedwith depressions to receive the supporting posts R and R to be describedbelow.

The testing element comprises a handle preferably made of wood which maybe of any length required for the operator to reach the place to betested. This handle may be hollow to provide a space for the leads K andK which are connected to the plug K at the resistance box. One end ofthe handle N is provided with a ferrule N which is threaded to receive acollar W, one of the leads K being connected with the metallic ferruleN. Concentric wire gauze jackets O O and 0 are mounted on the collar Wby flame-tight joints. These joints may be formed by flanging thejackets outwardly at the base and providing resilient washers betweenthe flanges. A perforated metallic bonnet P is mounted outside the gauzejacket and engages the collar W, compressing the washers between theflanges of the jackets. This bonnet serves to protect the gauze andsupplies a heat-absorbing capacity and a heat-radiating surface toassist in keeping the apparatus cool in case an inflammable mixtureshould be allowed to burn momentarily inside the inner gauze 0 Ametallic shield Q, may be secured to the bottom of the metallic bonnet Pto protect the apparatus from strong drafts which might have anobjectionable cooling effect on the hot filament. The metallic shield Q,is provided with a row of large perforations Q to permit the atmosphereto enter. A supporting post R having a U- shaped bend at the top and apointed end is provided inside the innermost gauze jacket 0 This iselectrically connected with the collar W and through the ferrule N tothe lead K Another supporting post R is mounted at or near the center ofthe testing element and slides through an insulating member W, beingurged upwardly by a spring S which engages a collar thereon below theinsulating member W. The spring S is electrically connected to the leadK but is insulated from the lead K by the wooden handle and theinsulating member W. In inserting the holder T the supporting post R isforced downwardly against the spring S, the cartridge is then insertedwith its upper depression engaging the point of the post R and the postR is then allowed to move upward to engage the lower depression .of theholder. After this has been done the gauze jackets are placed inposition and firmly held by screwing the metallic bonnet onto the collarW. The electrical circuit through the device is from the lead K throughspring S, supporting post R lower end piece Z, filament A, upper endpiece Z supporting post R collar W ferrule N back to the lead K Theoperation of the devices is as follows:

The battery is connected to the testing box at J and the testing memberis connected at K, the switches H and I are closed and resistance D isadjusted so that the instrument G shows no current flowing therebyindicating that the bridge is in balance. The switches H and I are thenopened and the device is taken into the atmosphere to be tested. Theswitch H is first closed to heat the filament A to such a temperaturethat any inflammable gases will be oxidized without catalytic action. Atemperature of 1,000 C. is satisfactory. Should any such gases bepresent the filament A will assume a temperature above that which itwould take in normal atmosphere and the resistance of the filament willbe increased. This will be evident by a deflection of the needle of Gupon closing the switch I. The instrument may be graduated so that theamount of gas present may be read directly or, if graduated as amillivoltmeter or a milliammeter, the amount of inflammable gas presentmay be determined from a table obtained by previous tests.

Should I so desire, I may construct various other embodiments of myinvention.

Thus, instead of using a portable instrument drawing current from aportable battery, the

gas testing member may be installed permanently at any desired locationin a mine and with any suitable source of current, such as the lightingcircuit, in which case suitable means for reducing the voltage should beprovided. In this case the testing box may be installed at a distancefrom the testing member, as on the outside of the mine, and I may, if Iso desire, install a recording millivoltmeter or milliammeter at G.

The testing filament instead of being mounted on a handle and connectedelectrically to the testing box by leads, may be installed in acombustion chamber formed in the testing box, in which case means mustbe provided for introducing a sample of the atmosphere to be tested intothe combustion chamber as, for example, a flexible tube terminating in apump, as a hand operated bulb pump. Moreover, the device, without changefrom the embodiment shown, may be operated by adjusting the variableresistance D to bring the needle of G to zero, the content ofcombustible gas being calculated from the resistance change required.

From the above description it will be evident that I have obtained adevice which has numerous advantages over the means heretofore used intesting for inflammable gases in atmospheres. Notwithstanding thenumerous methane detectors which have been proposed the only means atpresent widely employed for this use is the miners safety lamp. One ofthe advantages of my device is greater sensitiveness in that it plainlyindicates of methane while with the flame safety lamps experts canrarely detect less than 2%, and never less than 1%.

My device also has the advantage that by employing a handle of suitablelength it is possible to test the atmosphere in places such as in highrooms or under caved areas, which it would be unsafe to explore with alamp. My device lends itself well to permanent installation as arecording or alarm instrument,-

provision being made for the closing of a contactto an alarm device whenthe needle attains a predetermined deflection.

I claim:

1. In a testing system for determining the other supporting post againstsaid other recess.

2. In a testing element the combination of a base, a supportin post onsaid base having a U-shaped ointe end, an insulating member in said ase,a pointed supporting ost slidably mounted in said insulating mem er, askeleton holder containing a metallic filament en ged between saidsupporting posts, and resilient means urging said slidabl mountedsupporting plece against sai holder. v

3. In a testing element the combination of a base, a U-shaped supportingpost, a slidably mounted supporting post insulated from said base, aholder containing a metallic filament held between said supportingposts,-a

plurality of gauze jackets having flanged ends surroundingsaid holder,annular resilient members between said flanges and between the flange ofthe innermost jacket and the base, a perforated bonnet having a shoulderthereon, said bonnet cooperating with said base to compress theresilient annular members between said shoulder and said base.

In testimony whereof, I affix my signature.

ALBERT N. ERIGKSON.

